L-selectin shedding is activated specifically within transmigrating pseudopods of monocytes to regulate cell polarity in vitro

Proc Natl Acad Sci U S A. 2015 Mar 24;112(12):E1461-70. doi: 10.1073/pnas.1417100112. Epub 2015 Mar 9.


L-selectin is a cell adhesion molecule that tethers free-flowing leukocytes from the blood to luminal vessel walls, facilitating the initial stages of their emigration from the circulation toward an extravascular inflammatory insult. Following shear-resistant adhesion to the vessel wall, L-selectin has frequently been reported to be rapidly cleaved from the plasma membrane (known as ectodomain shedding), with little knowledge of the timing or functional consequence of this event. Using advanced imaging techniques, we observe L-selectin shedding occurring exclusively as primary human monocytes actively engage in transendothelial migration (TEM). Moreover, the shedding was localized to transmigrating pseudopods within the subendothelial space. By capturing monocytes in midtransmigration, we could monitor the subcellular distribution of L-selectin and better understand how ectodomain shedding might contribute to TEM. Mechanistically, L-selectin loses association with calmodulin (CaM; a negative regulator of shedding) specifically within transmigrating pseudopods. In contrast, L-selectin/CaM interaction remained intact in nontransmigrated regions of monocytes. We show phosphorylation of L-selectin at Ser 364 is critical for CaM dissociation, which is also restricted to the transmigrating pseudopod. Pharmacological or genetic inhibition of L-selectin shedding significantly increased pseudopodial extensions in transmigrating monocytes, which potentiated invasive behavior during TEM and prevented the establishment of front/back polarity for directional migration persistence once TEM was complete. We conclude that L-selectin shedding directly regulates polarity in transmigrated monocytes, which affirms an active role for this molecule in driving later stages of the multistep adhesion cascade.

Keywords: biglycan; calmodulin; invasion; leukocyte; migration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Adhesion
  • Cell Movement
  • Cell Polarity*
  • Cytoplasm / metabolism
  • Fluorescence Resonance Energy Transfer
  • Green Fluorescent Proteins / metabolism
  • Human Umbilical Vein Endothelial Cells
  • Humans
  • Inflammation
  • L-Selectin / metabolism*
  • Leukocytes / metabolism
  • Microscopy, Electron, Transmission
  • Microscopy, Video
  • Molecular Sequence Data
  • Monocytes / cytology*
  • Monocytes / metabolism
  • Phosphorylation
  • Serine / chemistry


  • L-Selectin
  • Green Fluorescent Proteins
  • Serine